The invention relates to a slip ring assembly for a rotor of an electric machine, an electric machine with a slip ring assembly, and a method for producing a slip ring assembly. Known slip ring assemblies of this type are normally comprised of two slip rings, which are supported by a holder made of insulating material. The two slip rings are each connected to an electrical connecting conductor, via whose ends one end can be fastened to an excitation coil of the rotor. One such slip ring assembly is known for example from Unexamined German Application DE 38 38 436 A1.
However, when using these and similar types of slip ring assemblies, previously unknown problems with rotary current generators, for which these types of slip ring assemblies are intended, have cropped up in connection with drive materials modified by vehicle manufacturers; in particular new materials for multi-V belts.
One phenomenon in this case is that, during rotational movement of the rotor, high electrostatic voltages build up, which discharge suddenly when an undefined limit is exceeded and which can thereby damage or even destroy the electronic components such as the regulator for the excitation coil. This voltage generation functions in accordance with the known “Van de Graaf generator.”
Various efforts have already been made to solve this problem. Thus, Unexamined German Application DE 101 18 004 A1 discloses a system in which the electrostatic voltage is dissipated from the electromagnetic iron part via the negative slip ring to the electrical ground of the electric machine, for example, via a conductive coating of the holder made of insulating material. The disadvantage of the attainments disclosed there is that smooth functioning of the excitation coil after assembly and after connection to the slip ring assembly is no longer reliable or cannot even been tested anymore. The consequence of this is that rotors that are untested or untestable in this respect are not recognized under some circumstances as damaged, and therefore are processed further in the cost-intensive manufacturing process even though they are long since defective goods.